New approaches for coherent and incoherent implementation of X-ray phase contrast imaging

• Main Author: Vittoria, Fabio Alessio
• Other Authors: Olivo, Alessandro ; Robinson, Ian ; Diemoz, Paul
• Published: University College London (University of London) 2016
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.746183

Two new x-ray imaging modalities exploiting the phase delay electromagnetic waves experience when travelling through matter are introduced in this work. The first, called beam tracking, allows the measurement of three different physical properties of an object: absorption, refraction and ultra-small-angle scattering. This is achieved by tracking the variations induced to a reference beam by a sample through a multi-Gaussian interpolation. Beam tracking can be implemented with both monochromatic, coherent radiation (available at e.g. synchrotron facilities) and polychromatic, incoherent radiation produced by standard laboratory sources. The nature of the three extracted signals allows the implementation of beam tracking in computed tomography, resulting in the three-dimensional reconstruction of the real and imaginary part of the sample refractive index, alongside its local scattering power. The second proposed method, called one dimensional ptychography, exploits the coherent properties of synchrotron radiation to retrieve the sample complex refractive index. The peculiar feature of this method is the strongly asymmetric beam used to illuminate the sample. Unlike standard ptychographic techniques, this enables scanning the sample in one direction only, which can lead to a possible reduction in exposure time when large field of views are covered. At the same time, ptychographic, sub-pixel resolution can be obtained only in the scan direction, while pixel-limited resolution is obtained in the orthogonal one. Prior to the introduction of these methods, the theoretical foundations are laid down, and the development of a fast and effective simulation software allowing their implementation is described.